Precipitation

Precipitation reactions

In a precipitation reaction two solutions are mixed together resulting in the formation of an insoluble solid called the precipitate.

Each of the solutions is composed of positive and negative ions. By convention the metallic ion is always named first. eg. sodium chloride is composed of positive sodium ions, Na+ and negative chloride ions, Cl-

In a precipitation reaction there is an exchange of partners creating a new set of positive and negative ions.

One group of these ions becomes more attracted to each other than they do to the water molecules. This produces an insoluble compound called the precipitate. The other set of positive and negative ions remains in solution.

Analogy of two couples on a dance floor.

Boys = (+) metallic ions and girls = (-) negative ions.

Fred and Jill + Jack and Wilma Fred and Wilma + Jack and Jill

On the dance floor there is a change of partners. Fred and Wilma are strongly attracted to each other. They leave their partners and unite together in a new relationship due to their strong attraction to one another. They form the solid precipitate. Jack and Jill, however, never quick make it together as an item. They are more strongly attracted to the water molecules than to each other.

A precipitation worksheet may be downloaded. The first page includes a precipitation practical experiment. The second page has equations only. The third page has the answers to the precipitation reactions.